This invention relates generally to trains and other rail vehicles and more particularly to systems and methods for distributed control of trains.
Train cars are commonly provided with a type of air brake system which functions to apply brakes on the car upon a pressure drop in a “brake pipe” that interconnects the cars and to release the air brakes upon a pressure rise in the brake pipe. The brake pipe is pressurized by a compressor in the locomotive. When braking is desired, a brake valve in the locomotive bleeds air from the brake pipe through an orifice.
Such air brake systems may be controlled by a system referred to as communication based train control (“CBTC”) or positive train control (“PTC”). In a PTC system, speed limits, temporary slow orders, movement authorities and other conditions are conveyed to a train cab using electrical signals on the rails, transponders, or wireless transmission so that aspect information can be directly displayed in the cab. An example of such a system is described in U.S. Pat. No. 5,533,695. An on-board computer scans for speed restrictions and, if a reduced speed or stop is ahead, calculates a braking distance or “braking curve” based on current speed, target speed, track gradient and train braking ability. The “target speed” and calculated “distance to target” may be displayed to the train crew. Then, the distance and time to where braking must start is calculated. In case of failure by the crew to take necessary actions such as decelerating or braking, the on-board computer can apply automated speed enforcement (i.e. penalty brake application) through an interface to the air brake system known as a “penalty valve”. Such PTC systems operate under the assumption that braking control is effected only by a lead locomotive or power unit, or by multiple connected power units which are at the front of the train. To assure safe braking, such systems usually assume a conservative worst-case scenario of braking effectiveness when determining a point to initiate penalty braking.
It is also known to control braking, throttle, and other train functions remotely using distributed power control systems for locomotives (hereinafter Distributed Power or DP systems or simply DP), in which the operation of one or more remote locomotives (or group of locomotives forming a locomotive remote) is remotely controlled from the lead locomotive of the train by way of a radio or hard-wired communication system. One such radio-based DP system is commercially available under the trade name LOCOTROL, and is described in U.S. Pat. No. 4,582,280, which enables communications among locomotives when connected together to form a consist or at spaced locations along the length of train when the locomotives are spaced apart by one or more railcars.
DP systems can provide shorter braking curves because the brake pipe is being bled down by two or more brake controllers (e.g. valve orifices) and the mean path length of the brake pipe from each car to a control valve (orifice) is reduced. They can also provide improved acceleration and/or tractive force. Known DP systems such as the one described above are highly reliable, but are not generally considered “vital”, i.e., their communications protocols do not conform to any specific standards for safety-critical train control operations that must be implemented in a fail-safe manner. If the communications link is interrupted performance may be downgraded.